Geometric burst kinetics — Fano factor F = 1 + b > 1 (super-Poissonian noise)
mRNA: — | Protein: — | Fano: —
Bursty gene expression (Paulsson 2005, Raj 2006): the promoter switches ON, producing a geometric burst of b mRNA molecules (mean burst size b, Fano factor F_m = 1+b). Each mRNA is translated into proteins before degrading. The protein distribution has Fano factor F_p ≈ 1 + bβ/(γ_m + γ_p) > 1. Blue = mRNA count, orange = protein/10 (scaled). Histograms show the steady-state distributions versus Poisson (dashed).